The present invention relates to microcards and more particularly to a method and system for connecting microcards to motherboards by means of an interposer.
A microcard is an electronic card assembly generally characterized by small size (e.g. PCMCIA or credit card size or less) and is typically densely populated with a variety of miniaturized SMT components like BGA (Ball Grid Array) modules, CSPs (Chip Scale Packages), Flip Chip or wire bond DCA (Direct Chip Attach) modules. A microcard may be populated on one or both sides of its substrate (board). FIG. 1 shows an example of a known microcard. Microcard 101 has a substrate 103 and a plurality of active devices 105 on both sides of substrate 103. Interconnection of the microcard to the xe2x80x9cexternal worldxe2x80x9d (e.g. motherboard 107 as shown in FIG. 1 or higher level assembly level) is obtained through connector 109a (male or female type) which fits into a corresponding connector 109b on motherboard 107. The connector hosts a plurality of metallic pins that are put in mechanical contact with the corresponding pins in the matched connector placed on the motherboard or other assembly.
In some of the recent electronic applications (e.g. microcards for mobile phones), the size of the electronic modules is becoming more and more critical. Many functions must be implemented in a very limited space, so that many active devices should be placed on a single module. As mentioned above, to increase the usable surface area on a substrate, it is known to use both faces of the substrate to mount active devices. For this reason a xe2x80x9cverticalxe2x80x9d mounting as described with reference to FIG. 1 has been the usual mounting method. However, it is evident that this method, with microcard 101 mounted perpendicularly with respect to motherboard 107, provides a relatively poor solution when space saving (e.g., of the overall height of the assembly) is an important requirement. Another drawback of this package is that handling by automatic pick and place systems, the usual machinery for assembling such components, is relatively difficult.
It is known to mount a microcard having electronic components on both sides, like the one shown in FIG. 1, by means of so-called xe2x80x9cgull wingxe2x80x9d connections. As shown in FIG. 2, using this method, the microcard, with its attached components can be mounted parallel to the motherboard, allowing the resulting package (usually called Flat Pack MCM) to be picked and placed by automatic handling machines. However the following drawbacks are introduced by these gull-wing connections: (1) the resulting package is very delicate from a mechanical point of view, due to the leads which can easily bend; (2) maximum size of the usable substrate is limited by intrinsic warpage of organic composites, which causes problems of lack of coplanarity; and (3) the assembly of peripheral gull-wing leads requires dedicated equipment.
It is an object of the present invention to provide a technique which alleviates the above drawbacks.
According to one aspect of the present invention, there is provided an interposer for electrically connecting an electronic card (a/k/a microcard) with a motherboard, the interposer including a first plurality of metal pads located on a first side of the interposer and electrically connectable to the circuit traces on the electronic card, a second plurality of metal pads located on a second side of the interposer and electrically connectable to the circuit traces on the circuit board, and a plurality of plated via holes therein extending from the first side of the interposer to the second side of the interposer for electrically connecting selected ones of the first plurality of metal pads to selected ones of the second plurality of metal pads when the interposer is positioned substantially between the electronic card and the circuit board to thereby electrically connect the electronic card to the circuit board.
As defined herein, the present invention allows the use of low cost, commonly available, base organic material to connect a microcard with a mother board, while realizing a stable operating assembly.
According to another aspect of the present invention, there is provided an electrical assembly including an electronic card having circuit traces thereon, a circuit board having circuit traces thereon, and an interposer positioned between the electronic card and the circuit board and electrically connecting selected ones of the circuit traces of the electronic card to selected ones of the circuit traces of the circuit board, the interposer including a first plurality of metal pads located on a first side of the interposer and electrically connected to the circuit traces on the electronic card, a second plurality of metal pads located on a second side of the interposer and electrically connected to the circuit traces on the circuit board, and a plurality of plated via holes therein extending from the first side of the interposer to the second side of the interposer for electrically connecting selected ones of the first plurality of metal pads to selected ones of the second plurality of metal pads when the interposer is positioned between the electronic card and the circuit board to thereby electrically connect the electronic card to the circuit board.
According to still another aspect of the present invention, there is provided a method of connecting circuitry on an electronic card to circuitry on a circuit board including the steps of positioning the circuit board having the circuit traces thereon in a first position, positioning an electronic card having the circuit traces thereon in a second position spacedly located from the first position of the circuit board, positioning an interposer between the electronic card and the circuit board, the interposer including a first plurality of metal pads on a first side thereof and a second plurality of metal pads on a second side thereof opposite the first side, the interposer further including a plurality of plated via holes therein electrically connecting selected ones of the first plurality of metal pads to selected ones of the second plurality of metal pads, and electrically coupling selected ones of the plurality of plated via holes to selected ones of the circuit traces on the electronic card to selected ones of the circuit traces on the circuit board.